The Japan Patent Publication No. S61-030556 provides a process for preparation of 2,4,6-trifluorobenzoic acid by hydrolyzing 3,5-dichloro-2,4,6-trifluorobenzonitrile using aqueous solution of sulfuric acid (40 to 90% by weight) at 140-200° C. followed by dechlorination in the presence of zinc.
The use of sulphuric acid at high temperature leads to the formation of several undesired side products which are required to be removed by purification processes which makes the process unsafe, tedious and uneconomical. 1,3,5-trifluorobenzene can also be used as an intermediate for preparation of 2, 4,6-trifluorobenzoic acid.
The Japan Patent Publication No. H04-224535 provides a process for preparation of 1,3,5-trifluorobenzene by decarboxylating 3,5-dichloro-2,4,6-trifluorobenzoic acid in the presence of organic amine such as tributylamine, trilaurylamine, dimethylaniline or trioctylamine at 150° C. After completion of the reaction, reaction mixture is treated with aqueous hydrochloric acid solution. The organic layer was separated and distilled to obtain 1,3-dichloro-2,4,6-trifluorobenzene. 1,3-dichloro-2,4,6-trifluorobenzene is then dechlorinated using hydrogen in the presence of a palladium-carbon catalyst and hydroxide or carbonate of alkali metals.
The use of hydroxide for dechlorination results in the formation of 1,3-dihydroxy-2,4,6-trifluorobenzene and use of alkali metal carbonates in dechlorination generates carbon dioxide and hydrochloride which results in catalyst deactivation and thus makes the process tedious, unsafe and expensive.
The use of organic amine in decarboxylation requires additional acid-base purification steps which makes the process tedious, uneconomic and unsafe. Thus there is a need to develop a robust, cost effective and safe process for preparation of 2,4,6-trifluorobenzoic acid and intermediates thereof.